Drawing of metal tubing

ABSTRACT

The method of controlling the wall thickness of a drawn metal tube by applying forces on the tube on opposite sides of the die whereby the tube leaves the die at a higher velocity than the velocity of the tube entering the die, and relating the velocities in a ratio to produce the desired wall thickness of the drawn tube.

United States Patent Ledebur [151 3,668,916 [451 June 13, 1972 [54] DRAWING OF METAL TUBING [72] Inventor: Harry C. Ledebur, Cranfield, Ohio [73] Assignee: Wean Industries, Inc.

[22] Filed: Jan. 19, 1970.

[2]] Appl. No.: 3,979

52 U.S.Cl. ..72/274, 72/284 51 m.c|......- ..B2lcl/00 5s FleldofSearch ..72/288,287,283,284,274

[56] References Cited UNITED STATES PATENTS 3,238,752 3/1966 Dilling ..72/2s3 3,572,078 3/1971 Kennedyet al ..72/l94 WALL t.

counuuous DRAW UNIT ENTERING TUBE DIAM- d,

CONTROLLED VELOCITY V.

Andrews et al ..72/284 Russell Primary Examiner-Charles W. Lanham Assistant Eraminer--Michael J. Keenan AttorneyMichael Williams [5 7] ABSTRACT The method of controlling the wall thickness of a drawn metal tube by applying forces on the tube on opposite sides of the die whereby the tube leaves the die at a higher velocity than the velocity of the tube entering the die, and relating the velocities in a ratio to produce the desired wall thickness of the drawn tube.

ZJA 17 PULL FORCE F DRAWING OF METAL TUBING BACKGROUND AND SUMMARY Heretofore, as far as I am aware, the wall thickness of a tube was controlled'during drawing operations by means of a plug disposed within the tube substantially in line with the draw die opening. The plug was either anchored on the end of a rod, or of the floating type wherein the plug is retained inside the tube in its proper position relative to the die by a shoulder on the plug bearing against the inside wall of the tube as the latter is reduced in diameter by the die.

In the case of the anchored plug the length of tube to be reduced was restricted to a practical length of the anchoring rod. This restriction was overcome by use of the floating plug, but plug life and proper lubrication of the floating plug presented problems. Perhaps the most severe limitation to use of a floating plug resulted in the drawing of welded tubes because the internal bead of a welded tube would score the plug and thereby unduly limit its life. Trimming of the internal bead of a welded tube not only necessitated an additional operation but also required caution. to prevent the bead trimmings from reaching the plug.

My invention eliminates the need for an internal plug in the drawing of tubing and thus provides many advantages over the prior art; For example, my invention makes it possible to draw tubing of long lengths, and eliminates the need for a plug anchor rod in the case of the fixed plug, or the need for plug lubrication and inspection, in the case of a floating plug. The tube drawing apparatus of my invention may be disposed in line with a tube welding mill to obtain higher production and closer O.D. tolerance and in such case the internal weld bead may be either trimmed or untrimmed depending upon the requirement of the finished product. Further, with this arrangement small diameter tubing of accurate diameter and wall thickness may be produced from a welded tube of larger diameter which is easier to weld and which facilitates trimming of the internal bead when required. Also, roll cost may be minimized by enabling production of various finished tube sizes from the same welded tube size.

My invention also makes it possible to efiect multiple reduction of long tubes through a series of dies and continuous draw units in line, in which case the wall thickness of the tube exit ing from each'die is controlled by the relative speed of the succeeding continuous draw unitv Such arrangement may be close-coupled, with a minimum of space between succeeding units. This is a decided advantage over draw units which require an internal plug to control the wall thickness at each die since the requirement of matching the speed of the draw units in the latter case becomes difiicult and may require considerably more space to the units.

My invention also makes it possible to draw long tubes at elevated temperatures since it is extremely difficult to properly cool and lubricate an internal plug under such conditions. Accordingly, it is the principal object of my invention to provide a method of controlling the wall thickness of a drawn tube, without the use of an internal plug.

allow looping of the tubing between DESCRIPTION OF THE DRAWING In the drawing accompanying this description and forming a part of this specification, there is shown, for purposes of illustration, an embodiment which my invention may assume, and

in this drawing the single figure is a schematic representation of such embodiment.

I DESCRIPT ION OF PREFERRED EMBODIMENT trolled by applying forces to the tube on opposite sides of the die whereby the tube leaves the die at a higher velocity than the velocity of the tube entering the die.

Any suitable means may be utilized to apply the forces to the tube, but I prefer to employ continuous draw units in preference to pinch rolls since the transport diameter of such draw units is more constant.

The drawing shows draw units l4, 15, such as caterpillar drives, on opposite sides of the die, each unit comprising a pair of endless belts or chains 16 on which traction lugs 17 are supported. The belts are driven in any suitable manner in the direction of the arrows l8, and the lugs 17 on respective pairs of belts cooperate to form an elongated rectilinear pass 19 in which the tube is gripped.

Any suitable means, such as variable speed drives (not shown) may be used to control the velocity of the units 14, 15, so that the velocity of one or both may be changed at will. In accordance with my invention, the unit 15 is driven at a higher velocity than the velocity of the unit 14.

I have disclovered that the wall thickness of the drawn tube may be accurately controlled, without use of an internal plug, by controlling the ratio of the velocities of the units 14, 15, and thus the velocities of the tube entering and leaving the die.

My discovery may be mathematically proven in the following manner:

The cross-sectional area A, of the tube prior to drawing is equal to 1rt,(d,-t,), where d, and t, are, respectively, the outside diameter and wall thickness of the tube prior to drawin g.

The cross-sectional area A of the tube after drawing is equal to m m -t where d and are, respectively, the outside diameter and wall thickness of the tube after drawing.

The elongation of the tube in the draw die is determined by I the equation I r/ F z/ i I where .4 and A are, respectively, the cross-sectionalareas of the tube before and after drawing, and V is the velocity of the tube leaving the die and V is the velocity of the tube entering the die.

From the above equations, the following mathematical equation may be evolved:

Thus having given values of 11,, d," and 2,, the wall thickness 1 of the drawn tube is determined soley by the ratio V,/V Therefore, the wall thickness of the drawn tube may be established by proper selection of the relative speeds of the draw units l4, 15.

Since the velocity of the draw unit 15 is higher than that of the unit 14, a pull force F, in the direction of the arrow 20 will be exerted on the tube leaving the die, whereas a pull force F, in the opposite direction (arrow 21) will be exerted on the tube as it enters the die 11. Thus, a stretching force is applied to the tube which reduces its wall thickness in direct relation to the ratio V /V It will be understood that the reduction in wall thickness of the drawn tubing will be limited by the maximum allowable longitudinal stress in the die.

I claim:

1. In the art of drawing a metal tube through a die without the use of a mandrel to reduce the outside diameter of the tube, the improved method of controlling the wall thickness of the drawn tube to a desired dimension, which comprises:

controlling tube movement by applying forces to the tube on opposite sides of the die whereby the tube leaves said die at a higher velocity than the velocity of the tube entering said die, and

relating the entering and leaving velocities of the tube in a t i t t t 

1. In the art of drawing a metal tube through a die without the use of a mandrel to reduce the outside diameter of the tube, the improved method of controlling the wall thickness of the drawn tube to a desired dimension, which comprises: controlling tube movement by applying forces to the tube on opposite sides of the die whereby the tube leaves said die at a higher velocity than the velocity of the tube entering said die, and relating the entering and leaving velocities of the tube in a ratio solely predetermined by the outside diameter and wall thickness of the tube before drawing and the desired wall thickness and reduced outside diameter of the drawn tube.
 2. The method of claim 1 wherein the ratio of the entering and leaving velocities of the tube are predetermined in accordance with the mathematical equation t2(d2-t2) t1(d1-t1) (V1/V2) where t2 is the desired wall thickness of the drawn tube, d2 is the reduced outside diameter of the drawn tube, and d1 and t1 are, respectively, the outside diameter and wall thickness of the tube before being drawn. 